Links from Nick Barr's Talk:
The Elements of User Experience (http://www.jjg.net/elements/pdf/elements.pdf)
The Lean Startup, Eric Ries (http://theleanstartup.com/)
Designed for Use, Lukas Mathis (http://www.amazon.com/Designed-Use-Create-Interfaces-Applications/dp/1934356751)
Pirate Metrics, Dave McClure (www.slideshare.net/dmc500hats/startup-metrics-for-pirates-seedcamp-2008-presentation)
MVP as cupcake (http://adaptivepath.org/ideas/cupcakes-the-secret-to-product-planning/)
Building a Princess Saving App (http://lunar.lostgarden.com/Mixing_Games_and_Applications.pdf)